Welcome IIBogie:
The freezing is usually caused by too much refrigerant being metered into the evaporator coil (inside) or not enough air passing over the coil to keep it in a condensation stage. It should condense moisture from the air and allow it to drain to the outside but when the air is not moving fast enough the coil cannot extract enough heat from the air to keep it from freezing.
Try to find out which speed the fan is running on and make sure it is on High. It takes more force from the fan to move cold air besides the need to keep plenty of warm air crossing the coils.
In rare cases, the refrigerant may be too high or too low. That means the compressor is getting liquid refrigerant back from the loop, which will overload and kill the compressor except where there is an accumulator to protect the compressor.
You said the system has been cleaned (that's number one) get the air moving like a howling Texas wind (that's number two), and lastly have the refrigerant pressures thoroughly tested. Too many mechanics want to say "It just needed a little gas". If it needed gas, it needs a leak reparied.
Glenn
